Will it be too windy? The forecast is for less windy conditions but with a chance of rain. Wind is a major preoccupation when you’re planning surveys to try and detect rails and other tidal marsh birds, most of which we do by ear. Wind of ten miles per hour is the upper limit for this field work, and calmer is better. It’s too windy now, but I think it will calm, so I tell my two volunteers, “Let’s go for it.” We’ll be able to start an hour before sunset and finish an hour after sunset—the time (along with sunrise) when the birds we survey are most vocal.
|Clapper Rail. Photo by Tom Grey / www.tgreybirds.com.|
PRBO has been intensively studying the population of Clapper Rails in San Francisco Bay since 2005, helping with the recovery of an endangered species whose numbers have plummeted to about 1,000 birds. The Clapper Rail is an indicator of healthy salt marsh, but there is a lot still unknown about this secretive creature. We do know that tens of thousands lived in San Francisco Bay before the marshy fringe was diked and drained for humans to use.
When the three of us arrive at the boat launch, tenuous sunbeams break the gray evening skies. We load up the boat and head into the choppy water of the Petaluma River. Loose flocks of grebes and coots part before us, and ducks scatter. Soon gulls from the nearby landfill come into sight, making their evening commute south to roosting areas.
After 15 minutes of bounding upriver, we arrive at the first survey station. It’s pretty quiet here, except for the Song Sparrows singing, chipping, and scolding throughout the pickleweed. There’s a distant hum of rush hour traffic, and ominous clouds over the hills north of Novato.
As we listen intently, the ten-minute survey period drags by. My watch beeps, and we move on to the next point. Almost immediately after I start the timer, we are greeted by the kikky-doo of a Black Rail. A little later, a second Black Rail chimes in.
Out of the corner of my eye, I see a dark shape hurtling over the water—fast, small, and determined—a Merlin! It whips low just above the pickleweed as sparrows dive for cover. It circles the boat and lands on top of a hunter’s blind less than 50 meters away. We watch it dart back into the marsh, and then we move on to the next point. Sunset is approaching.
|Len Liu records data on tidal marsh birds, from a boat on a calm late evening. Photo by Beth Huning / www.bethhuning.com.|
Kikky-doo! Another Black Rail. Again, kikky-doo—for nearly the entire ten minutes. I start to worry that we won’t hear any Clappers and wonder if something has happened to them here. Maybe the cold, wet weather killed some weak individuals? Hungry predators? Well, time to move on to the next point.
Then, kek-kek-kek-kek-kek way off in the distance. At least this won’t be a shut-out. Kek-burr! a Clapper Rail announces at the end of the point. The kek-burr call is thought to be a female advertisement, I explain to my companions.
At the next couple of points, right after sunset, the calling rate increases and we hear multiple Clappers with some more Black Rails mixed in.
Then the calls drop off rapidly, and by the last point, there are only a few Western Meadowlarks flying into the marsh for the night, a pair of Great-horned Owls hooting from the eucalyptus trees across the river, and ducks whirring through the darkness overhead.
There are dozens of other sites to monitor in PRBO’s ongoing study of the sensitive birds of San Francisco Bay’s tidal marsh. Accompanied by able volunteers, at sunrise or sunset, I’ll return many times to these tidal channels by boat—as often as the winds permit.